Thermal Management System with Heat Exchanger Blending Valve

ABSTRACT

A thermal management system and method of use are provided, the system including a heat exchanger, a refrigeration system, a coolant loop thermally coupled to the heat exchanger, and a by-pass valve that regulates the amount of coolant within the coolant loop that either passes through the heat exchanger or is diverted away from the heat exchanger. The coolant loop is thermally coupled to the battery pack of an electric vehicle.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of the filing date of U.S.Provisional Patent Application Ser. No. 61/539,997, filed 28 Sep. 2011,the disclosure of which is incorporated herein by reference for any andall purposes.

FIELD OF THE INVENTION

The present invention relates generally to thermal control systems and,more particularly, to a system for controlling the level of heatrejection from the coolant fluid in a vehicle cooling system to therefrigerant of a refrigeration system in the coolant-to-refrigerant heatexchanger of a vehicle thermal management system.

BACKGROUND OF THE INVENTION

The thermal management system of an automobile typically utilizesmultiple cooling loops, thus providing the desired level of flexibilityneeded to regulate the temperatures of multiple vehicle subsystems.System complexity may be dramatically increased if the vehicle utilizesan electric or hybrid drive train due to the need to regulate thetemperature of the vehicle's battery pack.

FIG. 1 is a high level diagram that illustrates the basic subsystemswithin the thermal management system 100 of a typical electric vehicle.In general, the thermal management system of such a vehicle includes arefrigeration subsystem 101, a passenger cabin HVAC subsystem 103, and abattery cooling/heating subsystem 105. In an alternate configurationillustrated in FIG. 2, the thermal management system 200 also includes adrive train cooling subsystem 201. Thermal management systems 100 and200 also include a controller 109. Controller 109 may be a dedicatedthermal management system controller, or may utilize the vehicle controlsystem in order to reduce manufacturing cost and overall vehiclecomplexity.

Refrigeration subsystem 101 is designed to be thermally coupled via oneor more heat exchangers to the other thermal subsystems comprisingsystems 100/200 whenever it is necessary or desirable to reduce thetemperature in the thermally-coupled subsystem. As such, in aconventional system the heat exchanger used to couple the refrigerationsubsystem 101 to the other thermal subsystems is sized to insuresufficient cooling capacity under maximum thermal loading conditions,i.e., the conditions in which the coolant temperature of the othercooling subsystem(s) is at the highest expected temperature and thermaldissipation requirements are set to the highest possible level.Generally, however, the thermal management system will not be requiredto provide this level of thermal dissipation. As a result, heat will beextracted from the coolant at a rate much greater than that being inputinto the coolant by the devices being cooled, leading to a rapid coolingof the coolant and large swings in coolant temperatures between coolantand components, and most importantly large swings in the amount ofrefrigerant cooling capacity used in reaction to the coolant temperatureinside the heat exchanger. In order to avoid such temperature andcooling capacity swings, a conventional thermal management system mayregulate the coolant flow rate through the heat exchanger by regulatingthe coolant pump speed. Alternately, a conventional thermal managementsystem may rely on the self-regulating aspects of the refrigerantthermal expansion valve based on the fixed super-heat setting.

While the conventional approaches of controlling the thermal dissipationprovided by the refrigeration system are adequate for many applications,an improved system for controlling thermal loads and thermal dissipationlevels is desired. The present invention provides such a thermalmanagement system.

SUMMARY OF THE INVENTION

The present invention provides a thermal management system for use in avehicle (e.g., an electric vehicle), the system comprising a heatexchanger, a refrigeration system thermally coupled to the heatexchanger, and a coolant loop thermally coupled to the vehicle's batterypack and thermally coupled to the heat exchanger via heat exchangerinlet and outlet ports, where the coolant within the coolant loop iscooled via the heat exchanger and the refrigeration system. The systemfurther comprises a by-pass valve that regulates coolant flow throughthe heat exchanger, where the by-pass valve is coupled to the coolantloop between the heat exchanger inlet and outlet ports such that theby-pass valve operates in parallel with the heat exchanger. The by-passvalve allows a first portion of the coolant entering the valve to flowthrough the heat exchanger while a second portion is diverted around theheat exchanger (i.e., by-passes the heat exchanger) and is thenrecombined with the first portion after the first portion exits the heatexchanger.

In other aspects of the invention: (i) the refrigeration system may becomprised of a gas-phase refrigerant compression system that includes arefrigerant, a refrigerant compressor, a condenser, and at least onethermal expansion valve; (ii) the refrigeration system may be coupled tothe heat exchanger via the thermal expansion valve; (iii) therefrigeration system may be thermally coupled to a HVAC subsystem, forexample using a cabin evaporator and a second thermal expansion valve;(iv) the thermal management system may include a controller and at leastone coolant temperature detector, for example mounted to monitor thetemperature of the coolant exiting the heat exchanger, where thecontroller regulates coolant flow through the heat exchanger using theby-pass valve based on the monitored coolant temperature; (v) thethermal management system may include a controller and at least onetemperature detector for monitoring battery pack temperature, where thecontroller regulates coolant flow through the heat exchanger using theby-pass valve based on the monitored battery pack temperature; (vi) therefrigeration system may be thermally coupled to a HVAC subsystem, forexample using a cabin evaporator, the thermal management system furtherincluding a controller and at least one coolant temperature detector andat least one HVAC evaporator outlet temperature detector, where thecontroller regulates coolant flow through the heat exchanger using theby-pass valve based on the monitored coolant temperature and HVACevaporator air outlet temperature; (vii) the circulation pump used tocirculate coolant through the coolant loop may be configured to operatein only two modes, where the first mode does not circulate coolant(i.e., the “off” mode) and the second mode circulates coolant at aconstant flow rate; (viii) the speed of the circulation pump used tocirculate coolant through the coolant loop may be modulated, for exampleusing pulse width modulation; (ix) the thermal management system mayinclude a heater coupled to the coolant loop, for example thermallycoupled to the coolant loop between the heat exchanger and the batterypack; and (x) the coolant loop may include a coolant reservoir.

In another aspect of the invention, a method of continuously regulatingthermal dissipation of a vehicle battery pack is provided, the methodincluding the steps of (a) monitoring the temperature of the coolantwithin a coolant loop, where the coolant loop is coupled to and inthermal communication with a vehicle battery pack and a heat exchanger,where the heat exchanger is in thermal communication with arefrigeration system, where the coolant is chilled as it passes throughthe heat exchanger by the refrigeration system, and where a by-passvalve coupled to the coolant loop splits the coolant entering theby-pass valve into a first portion that flows through the heat exchangerand a second portion that is diverted around the heat exchanger andrecombined with the first portion after the first portion exits the heatexchanger; (b) comparing the coolant temperature to a presettemperature; (c) increasing the first coolant portion and decreasing thesecond coolant portion if the coolant temperature is greater than thepreset temperature; and (d) decreasing the first coolant portion andincreasing the second coolant portion if the coolant temperature is lessthan the preset temperature. Steps (a) through (d) are preferablyperformed repeatedly as long as the vehicle is operating. Step (a) mayfurther be comprised of the step of monitoring coolant temperature ofthe first coolant portion after the first coolant portion exits the heatexchanger but before it is recombined with the second coolant portion.

In another aspect, the preset temperature corresponds to a preset rangeof temperatures and the method further comprises the step of neitherincreasing nor decreasing either the first or second coolant portions ifthe coolant temperature is within the preset range of temperatures.

In another aspect, the evaporator outlet temperature of the HVACsubsystem coupled to the refrigeration system is monitored, and step (c)of the method further comprises the steps of (c1) comparing a first HVACevaporator air outlet temperature determined before performing step c)with a second HVAC evaporator air outlet temperature determined afterperforming step c), and (c2) decreasing the first coolant portion andincreasing the second coolant portion if the second HVAC evaporator airoutlet temperature deviates from the first HVAC evaporator air outlettemperature by more than a preset amount, where step (c2) is performeduntil the first and second HVAC evaporator air outlet temperatures donot deviate by more than the preset amount.

In another aspect, passenger cabin temperature is monitored and comparedto a user input HVAC setting, and adjusting the HVAC system in responseto the passenger cabin temperature and the user input HVAC setting.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a high level diagram of the various subsystems used inthe thermal management system of a typical electric vehicle;

FIG. 2 provides a high level diagram of the various subsystems used inan alternate thermal management system for use in an electric vehicle;

FIG. 3 illustrates a preferred embodiment of the architecture of athermal management system utilizing the by-pass valve of the currentinvention;

FIG. 4 illustrates an exemplary feedback control process for use withthe coolant by-pass valve of the invention;

FIG. 5 illustrates an alternate feedback control process for use withthe coolant by-pass valve of the invention;

FIG. 6 illustrates an alternate feedback control process for use withthe coolant by-pass valve of the invention; and

FIG. 7 provides a perspective view of some of the components of acooling system in accordance with the invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In the following text, the terms “battery”, “cell”, and “battery cell”may be used interchangeably and may refer to any of a variety ofdifferent cell types, chemistries and configurations including, but notlimited to, lithium ion (e.g., lithium iron phosphate, lithium cobaltoxide, other lithium metal oxides, etc.), lithium ion polymer, nickelmetal hydride, nickel cadmium, nickel hydrogen, nickel zinc, silverzinc, or other battery type/configuration. The term “battery pack” asused herein refers to multiple individual batteries contained within asingle piece or multi-piece housing, the individual batterieselectrically interconnected to achieve the desired voltage and capacityfor a particular application. The terms “battery” and “battery system”may be used interchangeably and as used herein refer to an electricalenergy storage system that has the capability to be charged anddischarged such as a battery, battery pack, capacitor or supercapacitor.The term “electric vehicle” as used herein may refer to an all-electricvehicle, also referred to as an EV, a plug-in hybrid vehicle, alsoreferred to as a PHEV, or a hybrid vehicle, also referred to as a HEV,where a hybrid vehicle refers to a vehicle utilizing multiple propulsionsources one of which is an electric drive system.

FIG. 3 illustrates the components associated with an exemplary thermalmanagement system 300 that utilizes the present invention. It should beunderstood that the invention may be used with otherarchitectures/configurations.

The refrigeration subsystem shown in FIG. 3 uses a gas-phase refrigerantcompression system although it will be appreciated that other means(e.g., a thermo-electric cooler) may be used to cool the refrigeratedside of the heat exchanger used in conjunction with the battery coolingsubsystem. In the illustrated system, the refrigerant (e.g., R134a) ismaintained within refrigeration conduit 301. A compressor 303 compressesthe low temperature refrigerant vapor in the subsystem into a hightemperature vapor. The refrigerant vapor then dissipates a portion ofthe captured heat when it passes through condenser 305, thereby leadingto a phase change from vapor to liquid, where the remaining liquid is ata temperature below the saturation temperature at the prevailingpressure. Preferably the performance of condenser 305 is enhanced byusing a blower fan 307. The liquid phase refrigerant then passes througha receiver-dryer 309 that removes moisture from the condensedrefrigerant. In the preferred embodiment, and as shown, refrigerant line301 is coupled to a cabin evaporator 311 via a thermal expansion valve313, and to a heat exchanger 315 (also referred to herein as a chiller)via a thermal expansion valve 317. Thermal expansion valves 313 and 317control the flow rate of refrigerant into evaporator 311 and chiller315, respectively.

The heating, ventilation and cooling (HVAC) subsystem (i.e., subsystem103) provides temperature control for the vehicle's passenger cabin,typically via a plurality of ducts and vents. Preferably the HVACsubsystem includes one or more fans 319 that are used to circulate airthroughout the cabin on demand, regardless of whether the air is heated,cooled, or simply fresh air from outside the vehicle. To provide coolair, refrigerant is circulated through evaporator 311. To provide warmair during normal vehicle operation, the HVAC subsystem may utilize aheater 321, for example an electric heater (e.g., a PTC heater)integrated within evaporator 311. Although not shown, the HVAC subsystemmay include means such as a heat exchanger for transferring thermalenergy from either drive train subsystem 201 or battery subsystem 105 tothe HVAC subsystem.

The battery cooling subsystem (e.g., subsystem 105) includes a batterypack 323 coupled to a coolant loop 325 containing a coolant (i.e., aheat transfer medium such as water). In a typical electric vehicle,battery pack 323 is comprised of a plurality of batteries. One or morecirculation pumps 327 pump the coolant through battery pack 323.Circulation pump 327 may utilize a simple on/off operation (i.e., twooperational modes), or be varied, for example using pulse widthmodulation to achieve a range of pump speeds. Heat may be transferredfrom the battery pack to the coolant via a heat transfer plate, one ormore coolant conduits, or other means that are in thermal communicationwith the batteries within the pack. The coolant contained in loop 325 iscooled via heat transfer with the refrigerant in heat exchanger 315,assuming that the thermostatic valve 317 allows refrigerant from therefrigeration subsystem to pass through heat exchanger 315.Additionally, in a preferred embodiment of the invention, cooling loop325 is also thermally coupled to a heater 329 (e.g., a PTC heater), thusinsuring that the temperature of the batteries within battery pack 323can be maintained within the preferred operating range regardless of theambient temperature.

In the illustrated embodiment, cooling loop 325 also includes a coolantreservoir 331. Cooling loop 325 may also include a radiator (not shown)for discharging heat to the ambient atmosphere.

Although not shown in FIG. 3, as previously noted the thermal managementsystem may be configured to cool various components of the drive trainsuch as the electric motor, and/or cool high heat load electroniccomponents such as the power electronics, inverter and/or charger. Thesecomponents may be integrated within the battery cooling loop 325 orutilize a dedicated cooling subsystem.

In accordance with the present invention, a by-pass valve 333 isincluded in cooling loop 325. Valve 333 is located upstream of coolantinlet port 335 of heat exchanger 315, and therefore is placed inparallel with the heat exchanger 315 as shown. As a result of thisconfiguration, the amount of coolant that passes through heat exchanger315 versus by-passing the heat exchanger can be regulated. In thepreferred and illustrated configuration, the coolant that by-passes theheat exchanger is recombined with the chilled coolant exiting the heatexchanger at a junction 339. This approach provides control of coolantside heat rejection to the refrigerant system and allows a fixed coolanttemperature to be maintained in response to current thermal loadconditions which, in the preferred embodiment, depend on vehicleoperating conditions (e.g., battery pack temperature, ambienttemperature, etc.).

It will be appreciated that there are numerous techniques that may beused by the control system (e.g., controller 109) to control operationof by-pass valve 333 as well as the other aspects and components of thethermal management system of the invention. In general, the controlsystem uses a plurality of temperature sensors to monitor thetemperature within the various vehicle components (e.g., battery pack323), within one or more regions of the coolant loop(s) (e.g., coolantloop 325), and within one or more locations within the passenger cabin.In response to the monitored temperatures and the desired temperaturerange for the battery pack, cabin and other vehicle components, theamount of coolant passing through heat exchanger 315 is regulated as isoperation of the blower fans (e.g., fans 305 and 319), the heaters(e.g., heaters 321 and 329) and any other controllable features of thethermal system. While operation of the thermal control system may bemanually controlled, in the preferred embodiment controller 109 operatesautomatically based on programming implemented by a processor, either adedicated processor or a processor utilized in another vehiclemanagement system.

FIG. 4 illustrates an exemplary feedback control process for use withby-pass valve 333. In the illustrated process, upon systeminitialization (step 401) the temperature of the coolant is determined(step 403) using one or more temperature sensors 341. In the preferredembodiment temperature sensor 341 monitors the temperature of thecoolant after heat exchanger 315 and before battery pack 323. It shouldbe understood, however, that other temperatures may be used in thefeedback process. For example, the temperature of the coolant exitingthe battery pack 323 may be monitored or the temperature of the batterypack, or batteries within the pack, may be monitored directly.Additionally it will be appreciated that multiple temperature sensorsmay be used, either to provide redundancy or to allow temperatureaveraging.

Once the temperature has been determined, it is compared to a presettemperature or temperature range (step 405). Typically the presettemperature is set by the manufacturer although in some configurationsother parties such as a third party service representative may beallowed to set this temperature/temperature range. If the detectedtemperature is too high relative to the preset temperature/temperaturerange (step 407), then by-pass valve is opened further (step 409), thuspassing more coolant through heat exchanger 315 so that it may becooled. If the detected temperature is too low relative to the presettemperature/temperature range (step 411), then by-pass valve is closedfurther (step 413), thus diverting more coolant away from heat exchanger315. If the detected temperature matches the preset temperature or iswithin the preset temperature range (step 415), then no adjustment ismade to the by-pass valve setting (step 417). This feedback processcontinues throughout system operation.

In an alternate process illustrated in FIG. 5, in addition to monitoringheat load levels, for example by monitoring the temperature of thecoolant or the battery pack, the system also monitors the temperaturewithin the passenger cabin, thus allowing temperature swings within thepassenger cabin to be minimized even as the heat load levels applied tothe heat exchanger vary due to varying by-pass valve settings. This isespecially important during the onset of battery cooling. In thisembodiment, in addition to monitoring coolant temperature (step 403) thesystem also monitors cabin temperature (step 501), for example using acabin temperature sensor 343, and HVAC evaporator air outlet temperature(step 503). The cabin temperature is compared to the desired cabintemperature (step 505) where the desired cabin temperature may be inputby a user by adjusting a cabin temperature setting or by adjusting aHVAC control setting (e.g., to increase/decrease cabin cooling). If thecabin temperature is acceptable (step 507) then the system does notadjust HVAC output (step 509). If the cabin temperature is notacceptable (step 511) then the system does adjust HVAC output (step513). Similar to the previously described embodiment, the system alsocompares coolant temperature (or battery pack temperature, etc.) to thedesired temperature/temperature range (step 405). If the detectedtemperature is too low relative to the preset temperature/temperaturerange (step 411), then by-pass valve 333 is closed further (step 413),thus allowing more coolant to by-pass heat exchanger 315. If thedetected temperature matches the preset temperature or is within thepreset temperature range (step 415), then no adjustment is made to theby-pass valve setting (step 417). If the detected temperature is toohigh relative to the preset temperature/temperature range (step 407),then by-pass valve 333 is opened further (step 409), thus allowing morecoolant to flow through heat exchanger 315. After increasing coolantflow to heat exchanger 315, the HVAC evaporator air outlet temperatureof the HVAC system is compared to the HVAC evaporator air outlettemperature before valve 333 was adjusted (step 515). If the outlettemperature before and after by-pass valve adjustment is within a presetacceptable range (e.g., 3° C.), then the system simply continues tomonitor the temperatures of the coolant, cabin, etc. (step 517). If theoutlet temperature before and after by-pass valve adjustment is notwithin the preset range (step 519), then the coolant flow from theby-pass valve to the heat exchanger is decreased by a preset amount(step 521) and the before/after HVAC evaporator air outlet temperatureis once again checked (step 516).

FIG. 6 illustrates the process of FIG. 5, modified for use with a HVACsystem in which the user, instead of setting the cabin temperature andallowing the HVAC system to self-regulate, simply adjusts the output ofthe HVAC system. In this relatively common configuration, the user setsHVAC output by adjusting both blower fan speed and the relativetemperature of the HVAC output (i.e., in the range of “hot” to “cold”).Accordingly, in this configuration it is unnecessary to monitor cabintemperature (i.e., step 501) and use that temperature to automaticallyadjust HVAC output (i.e., steps 505-513). As these steps are skipped, inthe process illustrated in FIG. 6 after system initialization the systemcompares coolant temperature (or battery pack temperature, etc.) to thedesired temperature/temperature range (step 405). If the detectedtemperature is too low relative to the preset temperature/temperaturerange (step 411), then by-pass valve 333 is closed by an additionalamount (step 413), thus allowing more coolant to by-pass heat exchanger315. If the detected temperature matches the preset temperature or iswithin the preset temperature range (step 415), then no adjustment ismade to the by-pass valve setting (step 417). If the detectedtemperature is too high relative to the preset temperature/temperaturerange (step 407), then by-pass valve 333 is opened by an additionalamount (step 409), thus allowing more coolant to flow through heatexchanger 315. As in the process illustrated in FIG. 5, after increasingcoolant flow to heat exchanger 315, the HVAC evaporator air outlettemperature is compared to the HVAC evaporator air outlet temperaturebefore valve 333 was adjusted (step 515). If the outlet temperaturebefore and after by-pass valve adjustment is within a preset acceptablerange (e.g., 3° C.), then the system simply continues to monitor coolanttemperatures (step 517). If the outlet temperature before and afterby-pass valve adjustment is not within the preset range (step 519), thenthe coolant flow from the by-pass valve to the heat exchanger isdecreased (step 521) and the before/after HVAC evaporator air outlettemperature is once again checked (step 516).

While preferred feedback loops for operating by-pass valve 333 have beendescribed, it will be appreciated that other processes may be appliedduring the utilization of valve 333.

FIG. 7 provides a perspective view of some of the components of apreferred cooling system in accordance with the invention as describedabove.

It should be understood that identical element symbols used on multiplefigures refer to the same component, or components of equalfunctionality. Additionally, the accompanying figures are only meant toillustrate, not limit, the scope of the invention and should not beconsidered to be to scale.

Systems and methods have been described in general terms as an aid tounderstanding details of the invention. In some instances, well-knownstructures, materials, and/or operations have not been specificallyshown or described in detail to avoid obscuring aspects of theinvention. In other instances, specific details have been given in orderto provide a thorough understanding of the invention. One skilled in therelevant art will recognize that the invention may be embodied in otherspecific forms, for example to adapt to a particular system or apparatusor situation or material or component, without departing from the spiritor essential characteristics thereof. Therefore the disclosures anddescriptions herein are intended to be illustrative, but not limiting,of the scope of the invention which is set forth in the followingclaims.

What is claimed is:
 1. A vehicle thermal management system, comprising:a heat exchanger; a refrigeration system thermally coupled to said heatexchanger; a coolant loop thermally coupled to a battery pack, whereinsaid coolant loop is thermally coupled to said heat exchanger via a heatexchanger inlet port and a heat exchanger outlet port, wherein saidcoolant loop further comprises a circulation pump for circulating acoolant within said coolant loop, and wherein said coolant is cooled viasaid refrigeration system and said heat exchanger; and a by-pass valvefor regulating coolant flow through said heat exchanger, wherein saidby-pass valve is coupled to said coolant loop upstream of said heatexchanger inlet port and operates in parallel with said heat exchanger,wherein a first portion of said coolant passing through said by-passvalve flows through said heat exchanger, and wherein a second portion ofsaid coolant passing through said by-pass valve is diverted around saidheat exchanger and is then recombined with said first portion of saidcoolant after said first portion of said coolant exits said heatexchanger.
 2. The vehicle thermal management system of claim 1, whereinsaid refrigeration system is comprised of a gas-phase refrigerantcompression system comprising a refrigerant, a refrigerant compressor, acondenser, and at least one thermal expansion valve.
 3. The vehiclethermal management system of claim 2, wherein said refrigeration systemis thermally coupled to said heat exchanger via a first thermalexpansion valve.
 4. The vehicle thermal management system of claim 1,wherein said refrigeration system is thermally coupled to a vehicleheating, ventilation and cooling (HVAC) subsystem.
 5. The vehiclethermal management system of claim 4, wherein said refrigeration systemis thermally coupled to said HVAC subsystem via a cabin evaporator and asecond thermal expansion valve.
 6. The vehicle thermal management systemof claim 1, further comprising a controller and at least one temperaturesensor for monitoring a coolant temperature, wherein said controllerreceives said coolant temperature from said at least one temperaturesensor and regulates coolant flow through said heat exchanger via saidby-pass valve based on said coolant temperature.
 7. The vehicle thermalmanagement system of claim 6, wherein said at least one temperaturesensor monitors said coolant temperature for said first portion of saidcoolant after said first portion of said coolant exits said heatexchanger and before said second portion of said coolant is recombinedwith said first portion of said coolant.
 8. The vehicle thermalmanagement system of claim 6, wherein said at least one temperaturesensor monitors said coolant temperature after said coolant exits saidheat exchanger and before said battery pack.
 9. The vehicle thermalmanagement system of claim 1, further comprising a controller and atleast one temperature sensor for monitoring a battery pack temperature,wherein said controller receives said battery pack temperature from saidat least one temperature sensor and regulates coolant flow through saidheat exchanger via said by-pass valve based on said battery packtemperature.
 10. The vehicle thermal management system of claim 1,wherein said refrigeration system is thermally coupled to a vehicleheating, ventilation and cooling (HVAC) subsystem via a cabinevaporator, and wherein said vehicle thermal management system furthercomprises a controller and a first temperature sensor for monitoring acoolant temperature and a second temperature sensor for monitoring HVACevaporator air outlet temperature, wherein said controller receives saidcoolant temperature from said first temperature sensor and receives HVACevaporator air outlet temperature from said second temperature sensorand regulates coolant flow through said heat exchanger via said by-passvalve based on said coolant temperature and said HVAC evaporator airoutlet temperature.
 11. The vehicle thermal management system of claim1, wherein said circulation pump operates in only one of two modes,wherein said circulation pump operating in a first mode of said twomodes does not circulate said coolant through said coolant loop, andwherein said circulation pump operating in a second mode of said twomodes circulates said coolant through said coolant loop at a constantflow rate.
 12. The vehicle thermal management system of claim 1, whereinsaid circulation pump is operable over a range of pump speeds between aminimum pump speed and a maximum pump speed, wherein said circulationpump circulates said coolant through said coolant loop within a range offlow rates.
 13. The vehicle thermal management system of claim 1,further comprising a heater thermally coupled to said coolant loop,wherein said heater is thermally coupled to said coolant loop betweensaid heat exchanger and said battery pack.
 14. The vehicle thermalmanagement system of claim 1, said coolant loop further comprising acoolant reservoir.
 15. A method of continuously regulating thermaldissipation of a battery pack of a vehicle, the method comprising thesteps of: a) monitoring a coolant temperature of a coolant within acoolant loop, wherein said coolant loop is coupled to and in thermalcommunication with said vehicle battery pack, wherein said coolant loopis coupled to a heat exchanger, wherein said heat exchanger is inthermal communication with a refrigeration system, wherein said coolantis chilled as it passes through said heat exchanger by saidrefrigeration system, wherein a by-pass valve coupled to said coolantloop performs the step of splitting said coolant entering said by-passvalve into a first portion and a second portion, wherein said firstportion of said coolant passing through said by-pass valve flows throughsaid heat exchanger, and wherein said second portion of said coolantpassing through said by-pass valve is diverted around said heatexchanger and is recombined with said first portion of said coolantafter said first portion of said coolant exits said heat exchanger; b)comparing said coolant temperature to a preset temperature; c)controlling said by-pass valve to increase said first portion of saidcoolant and decrease said second portion of said coolant if said coolanttemperature is greater than said preset temperature; and d) controllingsaid by-pass valve to decrease said first portion of said coolant andincrease said second portion of said coolant if said coolant temperatureis less than said preset temperature, wherein said controlling steps areperformed automatically by a system controller.
 16. The method of claim15, further comprising the step of: e) repeating steps a)-d) throughoutoperation of said vehicle.
 17. The method of claim 15, wherein said stepa) of monitoring said coolant temperature further comprises the step ofmonitoring said coolant temperature of said first portion of saidcoolant after said first portion of said coolant exits said heatexchanger and before said second portion of said coolant is recombinedwith said first portion of said coolant.
 18. The method of claim 15,wherein said step a) of monitoring said coolant temperature furthercomprises the step of monitoring said coolant temperature after saidheat exchanger and before said battery pack.
 19. The method of claim 15,wherein said preset temperature corresponds to a preset range oftemperatures, said method further comprising the step of: e) controllingsaid by-pass valve to neither increase nor decrease said first portionof said coolant and to neither increase nor decrease said second portionof said coolant if said coolant temperature is within said preset rangeof temperatures.
 20. The method of claim 15, further comprising the stepof: e) monitoring an evaporator air outlet temperature from a heating,ventilation and cooling (HVAC) subsystem coupled to said refrigerationsystem, wherein said step c) of controlling said by-pass valve toincrease said first portion of said coolant and decrease said secondportion of said coolant if said coolant temperature is greater than saidpreset temperature further comprises the steps of: c1) comparing a firstHVAC evaporator air outlet temperature determined before performing stepc) with a second HVAC evaporator air outlet temperature determined afterperforming step c); and c2) controlling said by-pass valve to decreasesaid first portion of said coolant and increase said second portion ofsaid coolant if said second HVAC evaporator air outlet temperaturedeviates from said first HVAC evaporator air outlet temperature by morethan a preset amount, wherein step c2) is performed until said secondHVAC evaporator air outlet temperature does not deviate from said firstHVAC evaporator air outlet temperature by more than said preset amount.21. The method of claim 15, further comprising the steps of: e)monitoring a passenger cabin temperature; f) comparing said passengercabin temperature to a user input heating, ventilation and cooling(HVAC) setting; and g) adjusting a HVAC subsystem coupled to saidrefrigeration system in response to said passenger cabin temperature andto said user input HVAC setting.
 22. The method of claim 21, furthercomprising the step of: h) monitoring an evaporator air outlettemperature from said HVAC subsystem, wherein said step c) ofcontrolling said by-pass valve to increase said first portion of saidcoolant and decrease said second portion of said coolant if said coolanttemperature is greater than said preset temperature further comprisesthe steps of: c1) comparing a first HVAC evaporator air outlettemperature determined before performing step c) with a second HVACevaporator air outlet temperature determined after performing step c);and c2) controlling said by-pass valve to decrease said first portion ofsaid coolant and increase said second portion of said coolant if saidsecond HVAC evaporator air outlet temperature deviates from said firstHVAC evaporator air outlet temperature by more than a preset amount,wherein step c2) is performed until said second HVAC evaporator airoutlet temperature does not deviate from said first HVAC evaporator airoutlet temperature by more than said preset amount.